Systems and approaches for semiconductor metrology and surface analysis using Secondary Ion Mass Spectrometry (SIMS) are disclosed. In an example, a secondary ion mass spectrometry (SIMS) system includes a sample stage. A primary ion beam is directed to the sample stage. An extraction lens is directed at the sample stage. The extraction lens is configured to provide a low extraction field for secondary ions emitted from a sample on the sample stage. A magnetic sector spectrograph is coupled to the extraction lens along an optical path of the SIMS system. The magnetic sector spectrograph includes an electrostatic analyzer (ESA) coupled to a magnetic sector analyzer (MSA).
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method of determining wafer backside contact resistance, the method comprising: measuring a gap distance value of a surface of a wafer based on a comparison of a main capacitive sensor electrode driven with a first drive signal and a compensating capacitive sensor electrode driven with a second drive signal that is amplitude or phase shifted as compared to the first drive signal; measuring a value of the second drive signal; calibrating the value of the second drive signal to a reference impedance standard to determine an impedance value of the wafer to ground; and determining a contact resistance value for the surface of the wafer based on the gap distance value and the impedance value of the wafer to ground.
2. The method of claim 1 , wherein measuring the value of the second drive signal comprises driving the compensating capacitive sensor with the second drive signal that is a 180 degree shifted version of the first drive signal, and adjusting an amplitude of the second drive signal to obtain an amplitude value when a net current of the main capacitive sensor electrode and the compensating capacitive sensor electrode is zero, and wherein calibrating the value of the second drive signal to the reference impedance standard comprises calibrating the amplitude value to the reference impedance standard.
3. The method of claim 1 , wherein measuring the value of the second drive signal comprises driving the compensating capacitive sensor with the second drive signal that is a phase shifted version of the first drive signal, and adjusting a phase angle of the second drive signal to obtain a phase angle value when a minimum gap distance value is obtained, and wherein calibrating the value of the second drive signal to the reference impedance standard comprises calibrating the phase angle value to the reference impedance standard.
4. The method of claim 1 , wherein measuring the value of the second drive signal comprises varying a distance of the compensating capacitive sensor electrode from the surface of the wafer to obtain minimum gap distance value, and wherein calibrating the value of the second drive signal to the reference impedance standard comprises calibrating the minimum gap distance value to the reference impedance standard.
5. The method of claim 1 , wherein measuring the gap distance value comprises measuring the gap distance value when a net current of the main capacitive sensor electrode and the compensating capacitive sensor electrode is zero.
6. The method of claim 1 , further comprising: contacting a conductive electrode to the surface of the wafer; and directing a charged particle beam to a second surface of the wafer when the contact resistance value for the surface of the wafer is below a threshold value.
7. The method of claim 6 , wherein directing the charged particle beam to the second surface of the wafer comprises initiating a secondary ion mass spectrometry (SIMS) measurement of the second surface of the wafer.
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August 30, 2019
April 28, 2020
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